I. Field of the Invention
The present invention relates to a power-splitting transmission, by means of which there can be achieved a continuous variation from reverse gear to forward gear, passing through a particular position referred to as “neutral engaged”, wherein the travel speed of the vehicle is zero for any speed whatsoever of the internal combustion engine.
More precisely, its object is a power-splitting infinitely variable transmission on the basis of an electric variator and of a compound gearset, plus adjusting means that distribute the power between the input and output of the transmission differently depending on the mode of operation thereof.
II. Description of Related Art
Power-splitting transmissions can be based on three known principles or modes of power splitting. According to the first mode, known as “coupled-input”, the transmission is provided with a pair of power-splitting pinions for splitting the power at the input of the mechanism, and with an “assembler” epicyclic gearset, which recombines the powers at the output of the mechanism. The control element is a variator.
In power-splitting transmissions of the “coupled-output” type, there is provided, for example, a power-dividing planetary gearset at the input of the mechanism and a power-reassembling pair of pinions at the output of the mechanism, the control element again being a variator.
Finally, in power-splitting transmissions of the “two matching points” type, a first power-dividing epicyclic gearset can be placed at the gearbox input while a second power-reassembling epicyclic gearset is disposed at the gearbox output, the control element again being a variator.
The traditional infinitely variable transmissions (I.V.T.) use only one or two of these three operating principles.
From U.S. Pat. Nos. 5,558,589 and 5,935,035 there are known infinitely variable transmissions with two modes of operation combining at least two planetary gearsets, two mode-changing clutches and one electric variator, using the coupled-output power-splitting principle as the first mode of operation.
According to these patents, the mode-changing means are disposed outside the epicyclic gearsets.
The merit of having two modes of operation available lies in the increased range of transmission ratios and in the possibility of reducing the size of the electric variator, which can be composed on the basis of electric machines.
Nevertheless, in these known two-mode architectures, the mode changes are effected by multiple-disk clutches disposed on the output of the transmission, and for this reason are accompanied by torque jolts that are sensed as unpleasant by the users.
Another disadvantage of the architectures described in these patents lies in their complexity, in particular related to the presence of at least two clutches and one brake.
In previous French Patent Application 01-04690 in the name of the same Applicant, there was described a power-splitting infinitely variable transmission with two modes of operation, wherein the architecture is simpler than in the traditional transmissions of the same type, electric machines of small dimensions are used, and the mode changes thereof are not accompanied by any torque jolt. In this French Patent Application 01-04690, the mode changes are effected by acting on internal mechanical links of the transmission situated between the two gearsets. For this purpose, two reducing stages are disposed between the two epicyclic gearsets, these stages being respectively utilized in the first and in the second mode of operation. These two reducing stages are disposed in parallel between the gearsets on the same power train.
Application of these prior art teachings poses the problem of an infinitely variable transmission (I.V.T.) that is sufficiently compact that it can be disposed easily in a motive power unit of a vehicle.
In addition, such an infinitely variable transmission is difficult to use with an internal combustion engine that produces high torque and power, and it cannot be easily matched to the type of engine, whether it be gasoline or diesel.
The prior art leads to design problems for the hydraulic actuation circuit, which then poses major problems during repair and maintenance of the gearbox, particularly in the case in which the mode-changing system is constructed in the form of a multiple-disk clutch.
In the case in which the mode-changing system is provided with mechanical gearbox claws, there are problems for exchanging the mode-changing system inside the gearbox.
Finally, the matching of such a gearbox to a gasoline-powered internal combustion engine also poses a problem related to the speeds of rotation, which are very high, thus imposing large mechanical stresses on certain spinning elements.
In fact, the engine speeds of a gasoline engine are higher than those of a diesel engine, in such a way that certain elements of the gearbox spin very rapidly.
The problem posed by the rapid rotation of a gear part will be seen in particular in the description hereinafter.